Low Potassium (Hypokalemia) Can Occur During Pregnancy

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The term hypokalemia means that the concentration of potassium (K+) in your blood is below normal. Technically, this means below the low end of the normal reference range, which is usually 3.5 milliequivalent (mEq or mmol/L). Some laboratories use 3.6 or 3.7 as the cutoff point, but most people do not feel any symptoms, as long as the potassium concentration in their blood does not drop to 3.0, or lower. K+ of 2.5 mEq or lower represents severe hypokalemia. Because muscle tissue is very sensitive to changes in potassium levels, hypokalemia can affect the heart very seriously, leading to life-threatening situations.

During pregnancy, your potassium level can drop, due to vomiting, which eliminates acid, causing metabolic alkalosis (a pH in blood and body tissues that is too high). Metabolic alkalosis, in turn, causes potassium loss. Potassium levels also can drop, due to diarrhea, resulting from hormonal changes and stress of pregnancy. These changes flush potassium out of the body as water is lost. Potassium also drops due a rise in the level of a hormone called aldosterone. That’s because this hormone causes the kidneys to excrete more potassium.

Vomiting can be part of pregnancy, but there is also a more severe condition, called hyperemesis gravidarum (HG). This condition causes frequent vomiting and other problems. Additionally, certain antibiotics, diuretics (medicines that flush water from the body), and other medications can cause hypokalemia, as can excessive amounts of the hormone insulin, low levels of magnesium (a very common cause of hypokalemia), a water balance disturbance called diabetes insipidus, certain genetic kidney diseases, and low body temperature when it causes excessive shivering. Deficiency of potassium in the diet is not a common reason for hypokalemia, but it can exacerbate hypokalemia if you already have it.

Despite all of this, hypokalemia is rare during pregnancy, and most such cases are in the mild, symptom-free range (3.0-3.5 mEq). Hypokalemia is diagnosed after a blood sample is taken and tested for electrolytes, usually as part of a basic metabolic panel (BMP, also called chem-7 or a chem-8), or part of a comprehensive metabolic panel (CMP, chem-14). A woman with hypokalemia also requires electrocardiography (ECG). This is a common test of the electrical activity of the heart. In cases of low potassium, ECG often shows certain characteristic electrical changes. These changes are the result of the drop in potassium concentration outside of heart muscle cells.

In addition disrupting the heart muscle and the heart’s electrical conduction system, low potassium causes problems with skeletal muscles and with nerves. You feel the effects as muscle weakness, tremors, and cramps. During pregnancy, hypokalemia, especially due to HG, can lead to a severe, potentially fatal complication called rhabdomyolysis. Pregnant women may possibly be more prone to this condition compared with those who are not pregnant. There is also a severe pregnancy complication called hypokalemic paraplegia in pregnancy. Technically, this means paralysis due to low potassium. Woman with this condition may experience a range of problems, from weakness and numbing to complete paralysis. Severe hypokalemia causes cardiac arrhythmias, disruptions of the rhythm of the heartbeat. These disruptions can lead to strokes and sudden death. While severe hypokalemia ([K+ ] 2.5 mEq or below) is very rare in pregnancy, when it occurs it threatens the mother life, so it also threatens the life of the fetus.

Severe hypokalemia may be treated with intravenous potassium, along with fluids. For mild to moderate hypokalemia, your doctor may prescribe potassium pills, or juice with potassium. Ingesting a lot of potassium can give you gas (flatulence) as a side effect. If oral potassium is bothering you by causing gas, you can stop taking it, if your serum (blood) potassium level has reached the normal range. If you have been hypokalemic enough to suffer symptoms, if the symptoms have disappeared, and your potassium level has risen at least above 3.0 mEq, you may be able to hold off on the potassium pills and have your potassium levels monitored each day. When you have mild hypokalemia (K+ 3.0-3.5), it is acceptable to get your potassium purely from dietary sources, such as potatoes, orange juice, or bananas, unless your low potassium level is part of a downward trend, such that your doctor is concerned that it might get lower.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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